As is known in the art, high data rate optical fiber communication is achieved by subdividing the transmission spectrum of the fiber into many separate channels and then transmitting data rates compatible with electronic devices on each channel. This process is known as wavelength division multiplexing (WDM) and requires the use of optical filters, known as wavelength division multiplexers, in order to combine the lower data rate signals at the fiber input and to separate the data signals at the output. The current state of the art in WDM technology is what is commonly referred to as an arrayed waveguide grating (AWG). AWGs exhibit a competitive advantage over traditional thin film filters and bulk gratings since the AWGs are integrated on a chip, and are thus considerably smaller, more stable, and provide a greater degree of functionality.
In spite of the advantages listed above, AWGs have some limitations. Primarily, AWGs occupy large chip areas (>>10 cm2) and provide only moderate spectral efficiency. Integrated resonant devices such as ring resonators and photonic bandgap (PBG) or standing wave resonators occupy much smaller areas (<<10−3 cm2) and hold potential for greatly increased spectral efficiency. Resonators are essential optical devices for many other important optical components including lasers and nonlinear switches. A resonant cavity is characterized by its modal volume V and its quality factor Q where Q is a dimensionless lifetime, the time for the mode energy to decay by e−2π. Many useful devices require cavities that exhibit a very large Q and small volume V.
Three dimensional photonic bandgap (PBG) structures with singular defect sites have been shown to exhibit infinite quality factors while occupying small modal volumes. Similarly, the theoretical Qs of ring resonators can be very high. However, on account of the difficulty in fabricating the complicated geometries associated with three-dimensional PBG structures and ring resonators, considerable interest has been directed toward the simple one-dimensional case. Yet, upon reducing the dimensionality, PBG structures have been shown to radiate, which results in vastly diminished Qs, thereby limiting the devices' utility and effectiveness.
In view of the foregoing it would be desirable to provide integrated optic resonators that either minimize or totally eliminate radiation in one-dimensional PBG structures. It would be further desirable that the integrated optic resonators are manufacturable by planar fabrication techniques.